Traces of a neonicotinoid pesticide stimulate different honey bee colony activities, but do not increase colony size or longevity

• Published in: Ecotoxicology and environmental safety Vol. 231; p. 113202
• Main Authors: Meikle, William G., Colin, Théotime, Adamczyk, John J., Weiss, Milagra, Barron, Andrew B.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Inc 01.02.2022; Elsevier
• Subjects: Animals; Apis mellifera; Bees; Hive CO2; Insecticide; Insecticides - toxicity; Longevity; Neonicotinoids - toxicity; Nitro Compounds - toxicity; Pesticides - toxicity; Pollinator; Sublethal effect; Thermoregulation; Apis mellifera; Thermoregulation; Sublethal effect; Pollinator; Insecticide; Hive CO2; Hive CO
• ISSN: 0147-6513; 1090-2414
• DOI: 10.1016/j.ecoenv.2022.113202

How neonicotinoid contamination affects honey bees remains controversial. Studies have yielded contradictory results, and few have examined effects on colony development. Here we report the results of a comprehensive five-year study of the effects of the neonicotinoid imidacloprid on honey bee colonies. Colonies fed 5 ng/g (ppb) imidacloprid in sugar syrup showed increased brood production, lower temperature variability, higher CO2 production and had more foragers compared to control colonies fed unadulterated syrup, but treatment did not affect adult bee numbers or average hive temperatures, and did not increase food stores, daily food acquisition or colony survivorship. These results suggest that imidacloprid contamination increased colony metabolism without improving colony productivity, and helps explain why some studies have reported no, or even positive, effects of neonicotinoids. Effect sizes were generally small but that could be attributed at least in part to variability in uncontrolled factors such as weather. We provide an explanation for the diverse effects of pesticide contamination on honey bees, and an improved understanding of how colonies are impacted. •5 ppb imidacloprid in syrup increased brood, foragers and CO2 in bee colonies.•5 ppb imidacloprid in syrup reduced in-hive temperature variability.•5 ppb imidacloprid in syrup did not affect amounts of bees or food in bee colonies.•Effects of sublethal imidacloprid on bee colonies were consistent with hormesis.